How to protect Derry, Donegal from flooding

Last weeks flooding had a devastating impact in areas right across the North West. These vehicles were swept into the River Faughan close to Drumahoe.
Last weeks flooding had a devastating impact in areas right across the North West. These vehicles were swept into the River Faughan close to Drumahoe.

STEVE BRADLEY says ‘unprecedented’ weather events such as last week’s floods are likely to become more common in the future

Major flooding last week caused huge damage to homes, businesses and property and left the cityside of Derry almost entirely cut off.

Bridges and roads - such as this stretch at Glentogher in Inishowen -  were damaged in the floods.

Bridges and roads - such as this stretch at Glentogher in Inishowen - were damaged in the floods.

The Council described it as “an unprecedented event”, and the Met Office labelled it “extreme and exceptional.” Was this huge downpour really a one-off occurrence, however, or a taste of what the future holds?

What can be done to reduce the impact of flooding when it happens again? And will last week serve as a wake-up call to ensure that future flooding events aren’t baked into the very design of our city?

The bad news is that we’re likely to see more of these ‘extreme’ weather events in the future as a result of climate change. The good news in Ireland is that our winters will get milder and our summers warmer in the decades to come. The downside is that we’ll also face a greater frequency of heavy downpours, particularly in the summer months, as warmer air absorbs and carries more moisture.

So, the rules have changed. Weather which, in the past, would have been considered a rare once-in-a-hundred-year event will, with time, become more likely to happen once in every fifty, thirty or, even,twenty years. We can no longer base our expectations of the frequency of extreme weather in the future on what has happened in the past.

Inishowen was particularly badly affected by the floods. This bridge in Swan Park, Buncrana, was completely swept away.

Inishowen was particularly badly affected by the floods. This bridge in Swan Park, Buncrana, was completely swept away.

Although we can’t control extreme weather, we can work to reduce its impact when it happens. The best way to reduce the impact from any type of flooding is to ensure that people and property are not located in places likely to flood in the first place.

Floodplains are long-standing overspill areas used by rivers when heavy rain pushes too much water through their tributaries. And, as most towns and cities are located on rivers, floodplains can, therefore, play an important role in protecting human settlements downstream. That is a fact which some planners, councillors and housebuilders locally seem to have forgotten, however. Instead of being viewed as important natural defences, some centuries old floodplains in Derry and Inishowen have been built on and concreted over in recent years.

The Rivers Agency has a policy of not objecting to house building in areas where the risk of flooding is assessed as only once-in-a-hundred-years, so long as steps are taken to mitigate that risk.

But climate change is altering the frequency of extreme weather and shouldn’t we be building homes to last much longer than a century anyway? Plus, as Drumahoe park and ride illustrated last week, flooding can still occur even where mitigation steps like embankments have been used.

So, the most obvious way to reduce future flooding is to not locate people and property in areas with a tendency to flood in the firsty place. Yet Derry City & Strabane District Council’s Local Development Plan - the strategy which will guide all planning decisions here until 2035 - proposes to do just that. Under its section on flooding, the draft plan identified two potential options for the council to choose from : to either avoid all development in flood prone areas, or to let it happen “with appropriate mitigation”. The council’s preferred option is the latter. If further development is allowed in such areas over the next 20 years, we will be condemning communities to face repeats of the destruction, heartache and cost that was experienced last week.

There is an oversupply of land zoned for housing in the local council area already, with 500 hectares sitting undeveloped, so there is no housing need for permission to be given to build more homes on flood zones. Instead, the council should have an automatic presumption against further development in flood zones and should review the undeveloped land it has previously zoned for housing to understand how much of it is at risk from flooding. Existing floodplains that haven’t been developed could then be zoned as public amenity space/parks, enabling them to continue functioning as nature intended. And it would create a fantastic network of protected open spaces as the city of Derry continues to grow.

The planning choices we make today should reduce the risk of flooding for future generations, not increase it.

Nature can also help when it comes to reducing the impact of extreme weather events locally. The River Faughan travels for 60kms before reaching Drumahoe, and has numerous tributaries along the way - offering ample opportunities to reduce the speed at which rainfall runs off the Sperrins and enters the river. A recent study by the Environment Agency in England showed that planting trees around feeder streams can slow the rush of rainwater and reduce the height of flooding in towns by up to 20%.

Forested areas help the ground to function like a sponge, holding back and, then, releasing rainwater into the main stream much slower than bare hillsides or pasture do. Partial forestation of upstream areas would be a complicated process, however, requiring the consent of numerous landowners and not helped by the EU providing subsidies for farmers to clear trees and maintain land as open pasture.

Our towns and cities should also make smart changes to better cope with flooding. The principle again is to provide areas where excess rainwater can flow and be absorbed without causing damage elsewhere. Sustainable Urban Drainage Systems (SUDS) are increasingly common in UK cities. These are areas, sometimes no bigger than roadside strips, that are specifically designed to soak up water in the event of localised flooding. If done on a small scale, their contribution to flood alleviation would be helpful but limited; on a large scale, they can be expensive. The ideal approach would, therefore, be to add them when changes are being made to our build environment anyway.

Other urban changes to consider would include increasing the capacity of drainage systems when building new housing developments, and ensuring that existing urban drainage networks are regularly maintained to keep them free of blockages.

Derry City and Strabane District Council should view the events of the past week as an alarm call and ensure that their Local Development Plan doesn’t hard-wire future flood damage into the very design of our city. In that way at least one positive outcome would be guaranteed from last week’s terrible events.

Steve Bradley is a native of Derry who works as a regeneration consultant in England. He can be followed on Twitter at @bradley_steve